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Preliminary statement: in order to better understand how to use the sharpening machine and the features of the present invention, a short description of chain saws is necessary. Saws are generally formed by a series of driving chains with a thickness variable from 1.1 mm to 2.0 mm, but some special chains reach a thickness of 3.1 mm. See, FIG. 2. The links of these chains are joined to each other by a couple of jointing or connection links fixed by means of rivets allowing the articulation of the chain. See, FIG. 3. In the standard saw the driving links are connected to a connection link, which, in turn, is connected to a link with a special form having a tooth with an edge which is always turned towards the inside of the cutting chain; this tooth will be named right or left (FIGS. 2 and 3). Each tooth has a profile with an upper cutting angle and a lateral cutting angle (FIG. 4), these angles need to be perfectly sharpened, with the true and same angle either in case of right or left. In this way, the teeth come into the wood and remove shavings from the log in a perfectly identical way, which serves to reduce or prevent excessive stress during operation. In order to reinforce the hardness of the teeth, manufacturers typically coat the external surfaces of the teeth with a layer of chrome to give the metal a better resistance against the cutting stress on the wood.
During sharpening by use of grinding wheels the chrome-coated cutting part of the tooth may overheat. Because of the rubbing, some little metal feather edges and some little irregularities of the lateral and upper cutting angle are formed, but only on the internal part with respect to the rotation of the grinding wheel (e.g., that edge of the surface being ground at which the grinding wheel ceases to touch the tooth in revolution). That external part (which is the first one to be touched) remains perfectly regular and well sharpened.
Up to some years ago, the electric sharpening machines for chain saws were expected to have a double rotation of the motor and, consequently, of the grinding wheel connected to the motor, in order to obtain proper rotational direction for removing material from the tooth without creating feathers on the leading cutting edge; this rotational direction was always from the external part towards the inner part (FIG. 5, drawing 1) both in case of right and left teeth. If the feather edges and the irregularities are turned towards the inside of the tooth, the external cutting edge maintains the chrome layer and it presents a perfect cutting angle.
When sharpened in this manner, the cutting chain and the chain saw will work better when cutting through wood with less stress, thereby resulting in a more accurate cut.
The introduction of certain rules referring to operator safety in some jurisdictions (e.g., in Europe, rule CE 89/39 No. 73/23 No. 89/336, including integration, updates and amendments) forbids removal of material from the tooth of the saw in a manner that causes the sparks to fly towards the operator. Of course, potential for serious injury to the operator is present from grinding wheel breakage as well as removal of metal particles from the saw in the direction of the operator.
On the other hand the operator, for an accurate sharpening, needs to keep a good visibility on the contact point between the grinding wheel and the tooth. Accordingly, design of safety shields and other protective arrangements is difficult to accomplish without sacrificing function of the sharpener. For this reason present manufacturers have chosen a solution which provides only a single rotation direction for the electric motor (and consequently for the grinding wheel connected to the motor); this direction being opposite to the position of the operator. Due to this choice, the current sharpening machines are incapable of multiple positioning that would accomodate perfectly identical sharpening of the right and left teeth, respectively, of the chain saw cutting tooth.
The objects of the present invention are, therefore, the following:
1. To create an electric sharpening machine which assures maximum safety for the operator that complies with current European regulations in force, while at the same time allowing the sharpening of both right and left teeth of a saw by means of a rotation of the grinding wheel that turns in rotational direction from the external part of each tooth towards the inner part (following the upper and lateral cutting angle of the saw teeth).
2. To provide an electric sharpening machine that is easily adjustable and that accommodates reduction of waste of time by the operator.
3. To provide a sharpening device that during the sharpening can stop the cutting chain to be sharpened between the two jaws by a mechanical system, without any further manual actions by the operator.
Yet another feature of the device is the ability to stop the chain to be sharpened in the jaws of the vice, which is present at the base. By lowering the upper portion of the device, including the motor and the grinding wheel, about a first axis from an upper position in which it does not contact the chain, toward the base and lower position in which it may contact the chain, an actuating spring B10 is stressed acting an arm B11, which, in its turn, acts as a lever on the shaped block B12 exerting a pressure on the inner jaw through contact with the protruding part B13, causing it to adopt a closed configuration, which stops the tooth to be sharpened (FIG. 1).
The following describes in detail an example of an embodiment, but shall not be interpreted to limit the invention to the detail described.
In the manner above, the sharpening machine according to the invention solves the current problems concerning sharpening and safety, by solving contemporaneously the objects listed above 1 and 2. The present invention provides an electric sharpening machine for chain saws capable of correctly sharpening the teeth at any number of desired cutting angles within a given range; this system according to the invention allows rotation of an upper portion of the saw, including the motor and the grinding wheel about an axis that is parallel to the grinding wheel and immediately below the grinding wheel when the grinding wheel is in the perfectly vertical position. The chain to be sharpened can be progressed and automatically gripped by the lowering of the grinding wheel into a grinding position. The chain may be turned 180xc2x0 for grinding opposing teeth when the arm A2 (and hence the entire upper part) is rotated into a complimentary position. In this way it is possible to let the abrasive grinding wheel sharpen the saw teeth, both in case of left and right teeth, with rotation occurring towards the inner part of the teeth and opposite to the position of the operator for avoiding ejecting dangerous sparks and materials at the operator.